B-zone small lymphocytic lymphoma: a morphologic, immunophenotypic, and clinical study with comparison to "well-differentiated" lymphocytic disorders.

The pathologic, immunologic, and clinical features of five cases of B-zone small lymphocytic lymphoma (BZSLL), characterized by a nondestructive growth pattern with a selective and complete replacement of the B-zone areas of lymph nodes, were examined. These findings were compared with those of 13 cases of intermediate differentiated lymphoma/mantle zone lymphoma (ILL/MZL) and 20 cases of typical small lymphocytic lymphoma/chronic lymphocytic leukemia (SLL/CLL). B-zone SLL was characterized histologically by a deceptively benign pattern at a low magnification, the lymph node architecture being substantially preserved, in contrast to the ILL/MZL and SLL/CLL cases, in which complete effacement of the normal architecture usually could be observed. Moreover, in BZSLL the cellular population was rather uniform and lacked either a prolymphocytic component or the small-cleaved lymphoid cells often seen in SLL/CLL and ILL/MZL cases, respectively. The phenotypic profile of the BZSLL clonal cell population studied by the immunoperoxidase method and by single- and double-labeling flow cytometric analyses (SIg+, CD19+, CD20+, CD21+, CD22+, CD24+, CD35+, CD37+, CD74+, CD45+, CD45R+, MB2+, HLA-DR+, Leu-8+, CD9+/-, CDw75+/-, CD5-/+, CD23-/+, CD10-, FMC7-, PCA-1-, CD25-, CD38-, CD43-, CD3-) appeared to be fairly homogeneous and sufficiently distinct from that of ILL/MZL, based on the absence of FMC7 and CD38 molecules, and from that of SLL/CLL due to significantly stronger expression of SIgs (P less than .05), the higher reactivity with anti-CD9 and -CD22 antibodies (P less than .05), the lower reactivity with anti-CD5 and -CD23 antibodies (P less than .05), and the absence of CD25 determinants. Several clinical features of patients with BZSLL, including age group, advanced stage disease, and high frequency of bone marrow and peripheral blood involvement, were similar to those found in the other patients with ILL/MZL and SLL/CLL, but none of the BZSLL patients had an absolute lymphocyte count higher than 15.0 x 10(9)/L at presentation. Based on the architectural pattern, cytologic features, immunophenotypes, and hematologic findings, we conclude that BZSLL is an unusual variant of SLL that is primary in the lymph nodes and should be distinguished from ILL/MZL and CLL.